For modern telecommunications applications, apart from the electrical performance of the antenna other factors need to be taken into account, such as size, weight, cost and ease of construction of the antenna. Depending on the requirements, an antenna can be either a single radiating element or an array of like radiating elements. With the increasing deployment of cellular radio, an increasing number of base stations which communicate with mobile handsets are required. Similarly an increasing number of antennas are required for the deployment of fixed radio access systems, both at the subscribers premises and base stations. Such antennas are required to be both inexpensive and easy to produce. A further requirement is that the antenna structures be of light weight yet of sufficient strength to be placed on the top of support poles, rooftops and similar places and maintain long term performance over environmental extremes.
Antennas for cellular radio systems need to use low cost manufacturing methods. This is particularly important for microcellular and fixed wireless systems where antenna costs can be a significant part of the system costs by virtue of the requirement for a high deployment of base stations.
An antenna with integrated base station control electronics is one type of antenna that reduces the environmental impact of the base station. This type of antenna is known as an integral antenna and can potentially reduce costs both of the antenna and its installation. Further, by being built into the base station the environmental impact of the system is reduced by minimising the number and size of the separate parts. The antenna is also required to be lightweight.
Patch antennas comprise one or more conductive rectilinear or ellipsoidal patches supported relative to a ground plane and radiate in a direction substantially perpendicular to the ground plane. Conveniently patch antennas are formed employing microstrip techniques; a dielectric can have a patch printed upon it in a similar fashion to the printing of feed probes employed in layered antennas.
An antenna for fixed wireless access installations employing patch antenna arrangement is described in PCT Patent Application WO96/19844. The antenna comprises twelve patch elements arranged within a generally octagonal enclosure: the elements are printed on a dielectric sheet suspended between a reflector ground plane and the radome by dielectric spacers. The reflector ground plane has depressions corresponding in position with that of the printed radiating elements, whereby, inter alia, the microstrip feed lines are sufficiently proximate the ground plane to control the feed line radiation, whilst the spacing behind the radiating elements is sufficient to increase the bandwidth of the antenna. The outer dielectric is of formed expanded polystyrene and as such, this spacer will retain moisture which can reduce operating performance. The antenna has relatively large z-axis dimensions (i.e. dimensions in the direction of propagation).
A further type of antenna is known from U.S. Pat. No. 5,499,033 (Northern Telecom), which provides a linear array of radiating elements, employing an essentially tri-plate/layered antenna. Such antennas are typically used in groups with a radome arranged to cover and protect, singly or otherwise, the radiating elements.